The first lady had met Onassis in 1958, on his yacht, during a meeting between the president and Winston Churchill.

But Kennedy was determined that, during his wife’s 1961 visit to Greece, she should not meet the billionaire. With Bobby Kennedy, then the attorney general, beside him inside the White House, Kennedy told Mr Hill: “The attorney general and I wanted to make one thing clear and that is, whatever you do in Greece, do not let Mrs Kennedy cross paths with Aristotle Onassis.”

Mr Hill wrote: “At that time I had no idea why he would make such a request, but I simply answered: ‘Yes, sir, Mr President.'

President John F. Kennedy slumps down in the back seat of the Presidential limousine, Dallas.Credit:
AP Photo/James W. "Ike" Altgens

“I never did figure out a good explanation for President Kennedy’s request to keep Mrs Kennedy away from Aristotle Onassis, other than the fact Mr Onassis had been in legal trouble with the United States, and perhaps the president was concerned about repercussions should the press have gotten photos of Onassis and Mrs Kennedy together.

He changed his mind, however, following the death in August 1963 of their two-day-old baby, Patrick.

The first lady was distraught and Kennedy encouraged her to take up Onassis’s offer of the use of his yacht. On October 1 she travelled to Greece and spent a fortnight on board the Christina, Onassis’s luxury yacht, with nine double guest cabins.

And, in October 1968, the former first lady married Onassis on Skorpios, forfeiting her right to Secret Service protection and earning her considerable negative press. Onassis died in 1975, and his wife in 1994.